In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient and advanced through the aorta until the distal end is in the ostium of the desired coronary artery. Using fluoroscopy, a guide wire is then advanced through the guiding catheter and across the site to be treated in the coronary artery. An over the wire (OTW) balloon catheter is advanced over the guide wire to the treatment site. The balloon is then expanded to reopen the artery. The OTW catheter may have a guide wire lumen which is as long as the catheter or it may be a rapid exchange catheter wherein the guide wire lumen is substantially shorter than the catheter. Alternatively, a fixed wire balloon may be used. This device features a guide wire which is affixed to the catheter and cannot be removed.
To help prevent arterial closure, repair dissection, or prevent restenosis, a physician can implant an intravascular prosthesis, or a stent, for maintaining vascular patency inside the artery at the lesion. The stent may either be a balloon expandable stent or a self-expanding stent. For the former type, the stent is often delivered on a balloon and the balloon is used to expand the stent. for the latter type, the self-expanding stents may be made of shape memory materials such as nitinol or constructed of regular metals but of a design which exhibits self expansion characteristics. Self-expanding stents are typically constrained onto the delivery catheter by means of a retractable sheath covering the stent.
It is desirable in performing a PTCA or in implanting a stent to maintain a continuous blood flow across the catheter thereby providing a supply of oxygenated blood downstream from the catheter to prevent or minimize ischemic conditions in tissue distal or proximal to the catheter depending on the location of the catheter in the circulatory system. Specifically, as the catheter is moved into position in the area of a lesion, blood flow across the lesion may be cut off. Using a perfusion catheter, the catheter may remain in place in the region of the lesion for lengthy periods of time without damage to downstream tissue, thereby allowing for careful placement of balloon expandable or self-expanding stents and reducing the need for pre-dilation in order to maintain blood flow across the lesion.
Where the artery to be treated is the carotid artery, the stents used for implantation in the artery are larger than stents typically inserted in coronary arteries. It is desirable in delivering such stents to use a stent delivery system which is as large as is necessary in order to contain the stent within the stent canister region, but has a reduced shaft profile along the remainder of its length. This arrangement is preferred over a constant shaft size delivery system because it allows the physician to use the minimum size guide catheter shaft practical to allow passage of the stent canister while still retaining the ability to perform good contrast dye injections with the stent in position across the target lesion.
Because of the relative sizes of the stent canister and remainder of the catheter shaft, this type of stent delivery system configuration presents new catheter design challenges. The large stent canister, small proximal shaft arrangement, absent perfusion through the stent, would require the use of a pressurized saline flush through the side arm of the guide catheter hemostatic valve to prevent air from entering the guide catheter through the valve during passage of the stent delivery system through the guide catheter. Air is drawn into the guide catheter as a result of a piston effect. Quite simply, the stent canister displaces a large volume of blood as it is advanced through the guide catheter. Because the proximal shaft has a low profile in comparison with the canister, air may be drawn into the guide catheter behind the canister. In such a system, absent perfusion, it is desirable to have a pressurized source of fluid, such as saline solution, attached to the side-arm of the hemostatic valve to ensure that fluid, rather than air, makes up for the volume loss.
In addition to avoiding drawing air into the catheter because of the volume displacement effect, stent delivery catheters also need to be primed to eliminate any air contained within. Such priming, however, can be difficult, in particular in the region of the stent canister, primarily because of flow turbulence caused by the compressed stent, any rear stent bumpers, radio-opaque markers and the configuration of the tip of the catheter.
It is a goal of the present invention to provide a perfusion catheter capable of allowing perfusion across the stent canister portion of the catheter. It is a further goal of the present invention to provide a catheter whose design overcomes the piston effect and eliminates the necessity of having a pressurized supply of fluid to the catheter. It is a further goal of the present invention to provide a self-priming catheter.
These goals are provided for in the inventive perfusion catheter described herein in which perfusion occurs through the stent canister. Perfusion through the stent canister allows blood to readily pass to the proximal side of the stent canister thereby eliminating any canister volume displacement effect which in turn eliminates the need for a pressurized fluid side flush. Perfusion through the stent catheter also allows for self-priming of the stent canister thereby eliminating the need to manually prime the stent canister.
For the purposes of this disclosure, it should be noted that the word `mount` and variants thereon, as used in reference to mounting a medical device such as a stent on an inner tube, shall refer to the situation where the medical device is in physical contact with the inner tube, whether as a result of crimping or other processes of attaching the medical device to the inner tube. The word shall also encompass the retention of a medical device in place over an inner tube even absent contact between the medical device and the inner tube. For example, a self-expanding stent retained by a sheath over an inner tube shall also considered to be mounted over the inner tube.